1. Field of the Invention
This invention relates to sound reproduction systems with electrodynamic loudspeakers and closed housings. More particularly, the invention relates to a sound reproduction system for improved bass reproduction.
2. Prior Art
Conventional loudspeaker systems have an inferior bass reproduction if the housings are small. In small housings air compression forces will build up and hinder the movement of the radiating loudspeaker's membrane. These forces evolve from volume changes in the air inside the housing which are caused by the movement of the loudspeaker's membrane. The membrane compresses or decompresses the air and the resulting forces hinder the movement of the membrane. Being elastic forces they also increase the resonant frequency of the system.
To achieve a satisfying bass reproduction, large, impractical housings must be used, or different kinds of resonant boxes are employed. Often the driving signals are corrected in their frequency characteristic, or the loudspeakers are controlled by servo systems. All these solutions cause distortions or are impractical to use, or show a poor pulse response.
Another known method ( Tiefenbrun, U.S. Pat. No. 4,008,374) uses a second loudspeaker incorporated into the housing to simulate a larger volume. However this method just transfers the problems from the outer to the inner loudspeaker. To achieve satisfying results large housings must be used once again. Additionally, problems arise from distortions caused by phase differences between the movements of the membranes.